1. l Field of the Invention
This invention relates to a polyurethane composition less susceptible to deterioration by light. More particularly, it relates to a polyurethane composition which comprises a polyurethane obtained by reacting a polymeric diol containing polyoxyethylene chain, an organic alicyclic diisocyanate, an organic alicyclic diamine and hydrazine in a particular proportion and a particular dye. The polyurethane composition has an extremely good light resistance and is particularly useful as a component of artificial leather or as a coating material for fabric.
2. Description of the Prior Art
Polyurethanes have been used in a wide variety of fields, for example, as various foams ranging from cushion materials to structural materials, various molded articles, elastic fibers, coating materials, adhesives, artificial leathers and the like, because of their superior properties with respect to chemical resistance, abrasion resistance, resistance to cold weather, durability and the like, the development and advance of various processing techniques therefor and their unique elastic nature which covers a middle region between rubbers and plastics. Though polyurethanes have many advantages as above, they are inferior in light resistance and specifically have a disadvantage in that they are degraded when exposed to light, resulting in a decrease in tenacity and elongation. Particularly when a polyurethane is used as a surface coating material for fabric or as a component of artificial leather, its light resistance is of great importance.
Various attempts have heretofore been proposed to improve the light resistance of polyurethanes that is the most serious problem involved therein. Polyurethanes are formed by the reaction of a polyester, polyether or polycarbonate-type polymeric diol with an organic diisocyanate and an active hydrogen compound as a chain extender. It is well known that, when the organic diisocyanate used is an organic aromatic diisocyanate or the active hydrogen compound is an organic aromatic diamine, for example, the resulting polyurethane is susceptible to deterioration by light. Light resistance of polyurethanes can be improved by using an aliphatic or alicyclic organic diisocyanate and diamine in place of aromatic organic diisocyanate and diamine, respectively. Also it is known that the use of hydrazine as a chain extender provides a polyurethane having an improved light resistance.
On the basis of the above-mentioned knowledge, it is disclosed in German Pat. No. 2,252,280 (corresponding to U.S. Pat. No. 3,900,688 and British Pat. No. 1,418,550) that a polyurethane having an excellent light resistance can be synthesized by using a polycarbonate glycol as a polymeric diol, an aliphatic or alicyclic organic diisocyanate as an organic diisocyanate and a combination of an aliphatic or alicyclic organic diamine and hydrazine as a chain extender. However, the polyurethanes described in this patent are not adequately satisfactory with respect to light resistance.